Thecostraca is a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

of marine

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s containing over 2,200 described species. Many species have

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic larvae which become

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

as adults. The most important subgroup are the

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

s (subclass Cirripedia), constituting a little over 2,100 known species. The subgroup

Facetotecta Facetotecta is a poorly known subclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae, the "y- nauplius" and "y-cyprid" larvae. They are mostly found in the north Atlantic Ocea ...

contains a single genus, ''Hansenocaris'', known only from the tiny planktonic

nauplii Nauplius, Nauplia or Nauplios , may refer to : Greece-related * Nauplius (mythology), in Greek mythology, the son of Poseidon and Amymone, the father of Palamedes, and also the name of an Argonaut * Nauplia Nafplio ( ell, Ναύπλιο) is a ...

called "y-larvae". These larvae have no known adult form, though it is suspected that they are parasites, and their affinity is uncertain. Some researchers believe that they may be larval

tantulocarida Tantulocarida is a highly specialised group of parasitic crustaceans that consists of about 33 species, treated as a class in superclass Multicrustacea. They are typically ectoparasites that infest copepods, isopods, tanaids, amphipods and ostr ...

ns. No larval tantulocaridans are currently known. The group

Ascothoracida Ascothoracida is a small group of crustaceans, comprising around 100 species. They are found throughout the world, and are parasites on cnidarians and echinoderms. Ascothoracida was previously ranked as an order within the infraclass Cirripedia ...

contains about 110 species, all parasites of

coelenterate Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic ...

s and

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

Classification

This article follows Chan et al. (2021) and the World Register of Marine Species in placing Thecostraca as a class of

Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...

and in the following classification of thecostracans down to the level of orders. Previously, Thecostraca was considered a subclass of

Maxillopoda Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

. Significant changes in the organization of Cirripedia's orders, families, and genera were introduced in 2021 by Chan et al. and accepted by the World Register of Marine Species. Class Thecostraca Gruvel, 1905 * Subclass

Lacaze-Duthiers, 1880 ** Order

Laurida Laurida is an order of crustacean in the infraclass Ascothoracida. It consists of the following families and genera: * Lauridae ** ''Baccalaureus'' ** '' Laura'' ** '' Polymarsypus'' ** '' Zoanthoecus'' * Petrarcidae ** '' Introcornia'' ** ...

Grygier, 1987 ** Order

Dendrogastrida Dendrogastrida is an order of crustaceans belonging to the class Maxillopoda. Families: * Ascothoracidae Ascothoracidae is a family of crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals ...

Grygier, 1987 * Subclass

Grygier, 1985 * Subclass

Cirripedia A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive ...

Burmeister, 1834 ** Infraclass

Acrothoracica The Acrothoracica are an infraclass of barnacles. Acrothoracicans bore into calcareous material such as mollusc shells, coral, crinoids or hardgrounds, producing a slit-like hole in the surface known by the trace fossil name ''Rogerella''. Acr ...

Gruvel, 1905 *** Order Lithoglyptida Kolbasov, Newman & Hoeg, 2009 *** Order

Cryptophialida Cryptophialidae is a family of Acrothoracica The Acrothoracica are an infraclass of barnacles. Acrothoracicans bore into calcareous material such as mollusc shells, coral, crinoids or hardgrounds, producing a slit-like hole in the surface ...

Kolbasov, Newman & Hoeg, 2009 ** Infraclass

Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...

Müller, 1862 ** Infraclass

Thoracica Thoracica is an infraclass of crustaceans which contains the most familiar species of barnacles found on rocky coasts, such as '' Semibalanus balanoides'' and ''Chthamalus stellatus''. They have six well-developed limbs, and may be either stalked ...

Darwin, 1854 *** Superorder Phosphatothoracica Gale, 2019 (

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

) **** Order Eolepadomorpha Chan et al., 2021 **** Order

Iblomorpha Iblomorpha is a small order of barnacles in the class Thecostraca. There are only two families and about eight described species in Iblomorpha. Genera These families, subfamilies, and genera belong to the order Iblomorpha: * Order Iblomorpha Bu ...

Buckeridge & Newman, 2006 *** Superorder Thoracicalcarea Gale, 2015 **** Order

Calanticomorpha Calanticomorpha is an order of acorn barnacles in the class Thecostraca. There are 3 families and more than 90 described species in Calanticomorpha. Families These families and genera belong to the order Calanticomorpha: : Order Calanticomorpha C ...

Chan et al., 2021 **** Order

Brachylepadomorpha Brachylepadidae is an extinct family of barnacles in the order Brachylepadomorpha, the sole family in the order. There are about 7 genera and more than 20 described species in Brachylepadidae. Genera These genera belong to the family Brachylepad ...

Withers, 1923 **** Order

Archaeolepadomorpha Archaeolepadomorpha is an extinct order of barnacles in the class Thecostraca Thecostraca is a Class (biology), class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become Sessility (z ...

Chan et al., 2021 **** Order

Verrucomorpha Verrucomorpha is an order of asymmetrical sessile barnacles in the class Thecostraca. They are typically found in deeper and deep-sea habitats. There are 2 families and more than 100 described species in Verrucomorpha. Families These families be ...

Pilsbry, 1916 **** Order

Scalpellomorpha Scalpellomorpha is an order of acorn barnacles in the class Thecostraca Thecostraca is a Class (biology), class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become Sessility (zoology ...

Buckeridge & Newman, 2006 **** Order

Pollicipedomorpha Pollicipedomorpha is an order of pedunculated barnacles in the class Thecostraca. There are 3 families and more than 30 described species in Pollicipedomorpha. Families These families and genera belong to the order Pollicipedomorpha: : Order Poll ...

Chan et al., 2021 **** Order

Balanomorpha The Balanomorpha are an order of barnacles, containing familiar acorn barnacles of the seashore. The order contains these families: * Austrobalanidae Newman & Ross, 1976 * Balanidae Leach, 1817 (acorn barnacles) * Bathylasmatidae Newman & Ross ...

Pilsbry, 1916

Phylogeny

The following cladogram depicts the internal relationships of the Thecostraca as of 2021.

References

External links

* {{Taxonbar, from=Q150628 Arthropod classes